Pterodactyls

PTERODACTYLS. The extinct flying reptiles known as "pterodactyles" are among the most aberrant forms of animals, either living or extinct. Since the beginning of this century, when Blumenbach and Cuvier first described the remains of these curious creatures, they have occupied the attention of naturalists, and various opinions have been expressed as to their natural affinities. The general proportions of their bodies (excepting the larger head and neck) and the modification of the forelimb, to support a membrane for flight, remind one strongly of the bats, but the resemblance is only superficial; a closer inspection shows that their affinities are rather with reptiles and birds.

In all pterodactyles the head, neck, and forelimb are large in proportion to the other parts of the body (fig. 1). The skull is remarkably avian, and even the teeth, which

most of them possess, and which seem so unbird-like, are paralleled in the Cretaceous toothed birds of North America. Judging from the form of the skull, the brain was small, but rounded and more like that of a bird than that of a reptile. The position of the occipital condyle, beneath and not at the back of the skull, is another char-acter pointing in the same direction. The nasal opening is not far in advance of the large orbit, and in some forms there is a lachrymo-nasal fossa between them. The pre-maxillse are large, while the maxillae are slender. In certain species the extremities of the upper and lower jaws seem to have been covered with horn, and some forms at least had bony plates around the eye. The union of the post-frontal bone with the squamosal to form a supra-temporal fossa is a reptilian character. Both jaws are usually provided with long slender teeth, but they are not always present. The vertebral column may be divided into cervical, dorsal, sacral, and caudal regions. The centra of the vertebrae are proccelous,that is, the front of each centrum is cup-like and receives the ball dike hinder ex-tremity of the vertebra next in front of it. The eight or nine cervical vertebrae are always large, and are succeeded by about fourteen or sixteen which bear ribs. Probably there are no vertebrae which can be called lumbar. The sacrum consists of from three to six vertebras. The tail is short in some genera and very long in others. The sternum has a distinct median crest, and the scapula and coracoid are also much like those of carínate birds. The humerus has a strong ridge for the attachment of the pectoral muscle, and the radius and ulna are separate bones. There are four distinct metacarpals; passing from the inner or radial side, the first three of these bear respectively two, three, and four phalanges, the terminal ones having had

claws. The phalanges of the outermost digit are much elongated, and except in one doubtful form are always four in number. It is the extreme elongation of this outer digit, for the support of the patagium, which is the most characteristic feature of the pterodactyle's organization. A slender bone called the "pteroid" is sometimes seen extending from the carpal region in the direction of the upper part of the humerus. Some naturalists look upon the pteroid merely as an ossification of a tendon, corresponding with one which is found in this position in birds, while others are inclined to regard it rather as a rudimentary first digit, modified to support the edge of the patagium. The pelvis is small. In form the ilia resemble rather the ornithic than the reptilian type ; but the other portions of the pelvis are more like those of the crocodiles. The hind limb is small, and the fibula seems to have been feebly developed and fixed to the tibia. The hind foot has five digits in some forms, but only four in others. In the latter case the number of phalanges to each digit, counting from the tibial side, is two, three, four, five respectively. The long bones and vertebras, as well as some parts of the skull, contained large pneumatic cavities similar to those found in birds. There can be little doubt that the ptéro-dactyles had the power of sustained flight. The large size of the sternal crest indicates a similar development of the pectoral muscles and a corresponding strength in the arms. The form of the forelimb, especially its outer digit, indi-cates in no uncertain manner that it supported a flying membrane ; but within the last few years this has been more clearly demonstrated by the discovery of a specimen in the Solenhofen slates with the membrane preserved (fig. 2). The occurrence of ptérodactyle remains in marine deposits would seem to indicate that they frequented the seashore ; and it is tolerably certain that those forms with long and slender teeth were, in part at least, fish-eaters. Seeing, however, that the armature of the jaws varies considerably in the different genera, it is most likely that their diet varied accordingly. .

Ptérodactyles present so many avian peculiarities that it lias been proposed to place them in a special group, to be called Omithosauria, which would hold a position intermediate between Aves and Reptilia. On the other hand, ptérodactyles are thought by most authorities to have a closer relationship with the reptiles, and the different genera are placed in a separate order of the Reptilia, called Ptero-sauria. The most important genera are five. (1) Pterodactylus ; these have the jaws pointed and toothed to their extremities, and the tail very short. (2) Rhamphorhynchus (fig. 2) ; this genus has the jaws provided with slender teeth, but the extremities of both mandible and upper jaw are produced into toothless beaks, which were prob-ably covered with horn ; the tail is extremely long. (3) Dimor-phodon ; in this form the anterior teeth in both upper and lower jaws are long, but those at the hinder part of the jaw-s are short ; the tail is extremely long. (4) Pteranodon ; similar in most respects to Pterodactylus, but the jaws are devoid of teeth. In these four genera the outer digit of the manus has four phalanges. (5) Omi-thoptcrus ; this form is said to have only two phalanges in the outer digit of the manus ; the genus, however, is very imperfectly known, and it has been suggested that it may perhaps be a true bird.

The Pterosauria are only known to have lived during the Mesozoic period. They are first met with in the Lower Lias, the Dimor-phodon macronyx from Lyme Regis being perhaps the earliest known species. The Jurassic slates of Solenhofen have yielded a large number of beautifully preserved examples of Pterodactylus and R/iamphorhynchus, and remains of the same genera have been found in England in the Stoneslield slate. Bones of ptérodactyles have also been obtained in some abundance from the Cretaceous phosphatic deposits near Cambridge ; and their remains have been met with occasionally in the Wealden and Chalk of Kent. The genus Pteranodon is only known from the Upper Cretaceous rocks of North America. The Pterosauria were for the most part of moderate or small size (see fig. 1), but some attained to very con-siderable dimensions ; for instance, PJiamphorhynchus Bucklandi from the Stonesfield slate probably measured 7 feet between the wing-tips. But the largest forms existed apparently towards the close of the Mesozoic period, the ptérodactyles of the British Cretaceous rocks and the American Pteranodon being of still larger size : some of them, it is calculated, must have had wings at least 20 feet in extent.